Cumene is a valuable commodity chemical which is used industrially for the production of phenol and acetone. Cumene has for many years been produced commercially by the alkylation of benzene with propylene over a Friedel-Craft catalyst, particularly solid phosphoric acid or aluminum chloride. More recently, however, zeolite-based catalyst systems have been found to be more active and selective for propylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606 describes the use of MCM-22 in the alkylation of benzene with propylene.
Typically, the zeolite catalysts employed in hydrocarbon conversion processes, such as aromatics alkylation, are in the form of cylindrical extrudates. However, it is known from, for example, U.S. Pat. No. 3,966,644 that shaped catalyst particles having a high surface to volume ratio, such as those having a polylobal cross-section, can produce improved results in processes which are diffusion limited, such as the hydrogenation of resid.
Moreover, it is known from U.S. Pat. No. 4,441,990 that a polylobal catalyst particle having a non-cylindrical centrally located aperture can reduce the diffusion path for reagents and the pressure drop across packed catalyst beds while minimizing catalyst loss due to breakage, abrasion and crushing. In particular, Example 8 of the '990 patent discloses that hollow trilobal and quadrilobal ZSM-5 catalysts are more active and selective for the ethylation of benzene at 770° F. and 300 psig pressure than solid cylindrical catalysts of the same length. Under these conditions, the reagents are necessarily in the vapor phase.
Recently, attention has focused on liquid phase alkylation processes for producing alkylaromatic compounds, since liquid phase processes operate at a lower temperature than their vapor phase counterparts and hence tend to result in lower yields of by-products. Work by the present inventors has shown that shaped catalyst particles, such as those disclosed in U.S. Pat. Nos. 3,966,644 and 4,441,990 show little or no advantage when used in the liquid phase ethylation of benzene. Surprisingly, however, it has now been found that shaped catalyst particles can yield improved results in the liquid phase propylation of benzene to produce cumene.